Light-emission performance of silicon nanocrystals deduced from single quantum dot spectroscopy

Abstract

Spectra of individual silicon nanocrystals within porous Si grains are studied by the wide-field imaging microspectroscopy and their ON-OFF blinking is detected by the confocal single-photon-counting microscopy. Observed spectral and blinking properties comprise all features reported before in differently prepared single Si nanocrystals (SiNCs). Former apparently contradictory results are shown to be due to different experimental conditions. When the effect of dark periods (OFF switching) is removed the common ultimate photoluminescence properties of SiO2 passivated SiNCs are found, namely the quantum efficiency (QE) of about 10-20% up to the pumping rate corresponding to one exciton average excitation per quantum dot. At higher pump rates the QE is slowly decreasing as the 0.7th power of excitation. This is most likely due to Auger recombination which, however, seems to be weakened compared with measurements of nanocrystal assemblies. We conclude that SiNCs may be pumped above one exciton occupancy to yield a higher light emission, being advantageous for applications. © 2008 WILEY-VCH Verlag GmbH & Co. KGaA.